WAMP is an acronym for the combination Microsoft Windows, Apache httpd, MySQL and one or more of Perl, PHP and Python. The term is modelled after the more well-known LAMP, which refers to the all-open source/free software approach which uses Linux instead of Windows.
This article is about a server. A great majority of websites are run by a trio of services - Apache, MySQL and PHP. Apache is the web server, which handles browser requests and sends the information across the internet to your browser. PHP is the programming language that many sites are written in - this creates dynamic content which in turn is sent to Apache, which sends the data to your browser. And finally, MySQL is the database which stores the information for programs. PHP is used to access this database.